1. Field of the Invention
This invention relates to an improved sucker rod made of plastic materials, and more particularly, to a fiber reinforced plastic sucker rod in which the threads at each end of the sucker rod are of increased strength, the fibers being continuous through the apex portion of the threads, and to a method of manutacturing such improved sucker rod, and couplings used therewith.
2. Description of the Prior Art
Steel sucker rods used to transmit power between a bottom hole reciprocating pump and above ground means to cause the reciprocation have long been used in the production of oil or other fluids from subterranean wells, and are now standard in diameters, length and joints.
Fiber reinforced sucker rods have been manufactured for some time, but because of limitations in existing products, they have not been universally employed in the petroleum industry. Attempts to manufacture fiber reinforced sucker rods with integral internal and external threads with strength equal to the rod body have been unsuccessful. Furthermore, it is not practical to machine a thread into a resin fiberglass laminated sucker rod or other types of fiber reinforced sucker rods because machining cuts the reinforcing fibers and weakens the structures to such an extent that in use the threads break, thus being of no value as a coupler.
To overcome this problem, others have employed plastic and fiberglass sucker rocs having metal couplings affixed to each end of the rod. This technique has not been universally successful due to the lack of uniformity and predictability and the higher manufacturing costs. Also the metal parts can only be attached to the surface fibers of the rod which bypasses the main strength of the fiber bundle in the rod. Although, the high coefficient of friction characteristic of fiber reinforced plastic overcomes the problem of metal unthreading in service due to its low coefficient of friction, the metal fittings attached to the rod also cause increase in the weight of the rods and susceptibility to corrosion.